John G. Sargent was born in Ludlow, Vermont on October 13, 1860, the son of John Henmon Sargent and Ann Eliza Hanley.[2] He graduated from Black River Academy, and received his degree from Tufts College in 1887.[3][4] Sargent was married to the former Mary Lorraine Gordon on August 4, 1887.[5] They had a daughter, Gladys Gordon Sargent.[6]

In addition to practicing law, Sargent was active in the insurance business, served as President of the Ludlow Savings Bank, and was a member of the board of directors of several railroads and other corporations.[8][9][10]